Description of a 111-kb pathogenicity island (PAI) encoding various virulence features in the enterohemorrhagic E. coli (EHEC) strain RW1374 (O103:H2) and detection of a similar PAI in other EHEC strains of serotype O103:H2

Human infections with enterohemorrhagic E. coli (EHEC) strains of serotype O103:H2 are of increasing importance in Germany. As bovines are the principal EHEC reservoir behind the occurrence of human infections, we analyzed a pathogenicity island (PAI IRW1374) of bovine O103:H2 strain RW1374 to identify putative virulence features. This PAI IRW1374 harbors a functional 34-kb locus of enterocyte effacement (LEE) core region and has a total length of 111 kb. About 43 kb upstream of the LEE core a gene cassette consisting of efa1/lifA gene and flanking IS elements suggests another putative transposon within the PAI IRW1374. In addition, the ent gene, encoding a Shigella ShET-2 enterotoxin homologue, is present about 57 kb upstream of the LEE core. This PAI is therefore a complex assembly of various virulence determinants including the efa1/lifA and the ent gene resembling O157:H7 PAI OI-122/SpLE3 as well as the LEE core region. An integrase gene on the very left end of PAI IRW1374 is disrupted by an IS629 homologue. In an attempt to mobilize the LEE core we performed conjugation, transformation and transduction experiments. We were, however, unable to mobilize the whole or even single regions of PAI IRW1374. Comparative studies with other strains of serotype O103:H2 isolated from humans, bovines and food showed that they all harbored a similar pheV-inserted PAI including the virulence genes ent and lifA/efa1 as well as the large virulence-associated plasmid encoding the EHEC hemolysin. This combination of several virulence factors confirms the complex virulence of O103:H2 EHEC and may at least partly explain the high virulence of this EHEC serotype in humans.